%I
%S 1,9,216,15444,3281472,2067554808,3863711228544,21415460458704264,
%T 352065294244909032696,17166897737612437082259600,
%U 2482751631736501357900013730432,1064995044786220639044258688726569096
%N 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one, two or three horizontal and vertical neighbors
%H R. H. Hardin, <a href="/A211044/b211044.txt">Table of n, a(n) for n = 1..16</a>
%e Some solutions for n=4
%e ..1..1..0..1....1..1..1..1....0..1..1..2....0..0..2..1....0..2..0..1
%e ..1..2..2..2....1..0..2..1....1..0..1..2....0..0..2..2....2..2..1..2
%e ..0..2..0..1....1..2..0..0....1..1..1..2....2..2..2..0....0..1..2..2
%e ..1..2..1..0....1..1..0..1....2..2..2..2....1..2..0..2....1..2..2..2
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 30 2012
